The present invention relates to the field of workpiece holding and locating devices for precision machining operations. More particularly, this invention relates to a device for precisely and adjustably securing a workpiece to a machining table having T-slots.
In order to machine a workpiece on a modern numerically controlled machine tool, it is necessary to precisely locate a reference feature of the workpiece, such as a side edge, or diameter, etc. relative to a known or "home" position on the machine tool once the workpiece has been mounted on the machine. Then other features can be machined into the workpiece in predetermined relation to the referenced feature. Before mounting the workpiece on the machine, it is conventional to mount cubical bases or fixture plates to the T-slots of the machine table using bolts and T-nuts. The T-nuts slidably mount in the T-slots of the table. Once the setup person or operator places the base or fixture plate on the machine, it is carefully positioned using conventional techniques and dial indicators before it is secured to the table. The bases or fixture plates then receive other fixture components, such as clamps and jigs to hold the workpiece in position. Sometimes the other clamping components must also be carefully positioned and checked with dial indicators to make sure they are in the proper position.
Two methods of mounting the clamps, etc. to the bases or fixture plates are typically utilized. In both methods, the base or fixture plate has an exposed upper or outer surface (different from the surface mounted to machine table). In the first method, a set of parallel T-slots are formed in the exposed surface and the clamps and jig mount with bolts and T-nuts to the exposed surface. In the second method, an exposed surface of the bases or fixture plates includes a very precise predetermined pattern of equally spaced threaded holes for positioning clamps, fixtures, or jigs to hold the workpiece in place.
Because of the tolerance stackup involved in these conventional multiple-component workpiece holding devices, the features of the bases or fixture plates must be machined to stringent tolerance requirements. Thus, bases and fixture plates are costly components in conventional workpiece holding systems. Furthermore, these conventional multiple-component workpiece holding devices and methods require considerable setup time and effort.
Therefore, a primary objective of the present invention is the provision of an improved workpiece locating and holding device.
Another objective of this invention is the provision of a workpiece holding device that mounts directly to the machine table and thereby eliminates the need for a separate base or fixture plate.
Another objective of this invention is the provision of a workpiece holding device that spaces the workpiece a known distance away from the table surface so as to provide a known clearance for cutting tools between the table and the workpiece.
Another objective of this invention is the provision of a workpiece holding device and method that reduces the time and effort required for setup.
Another objective of this invention is the provision of a workpiece holding device that is readily adaptable to a variety of different machine tables having different sizes of T-slots.
Another objective of this invention is the provision of a workpiece holding device that accurate and reliable in use because it is less sensitive to tolerance stackup and dimensional variation of its components.
Another objective of this invention is the provision of a workpiece holding device that is economical to produce and easy to use.
These and other objectives will be apparent from the drawings, as well as from the description and claims that follow.